For the purposes of the present application the following word(s) and expression(s), unless otherwise indicated, shall be understood as having the meaning indicated in respect thereto:
the word "soil" and the like (whether as noun, adjective, etc.) shall be understood as referring to unconsolidated mantle (whether natural or man made) including:
material disposed on dry land masses; PA1 material which is wholly mineral or which in addition to mineral material, has an organic matter portion derived for example from plant or animal sources; organic material such as plant material would usually form part of the courser aggregate material as described hereinafter and would include, for example, tree stumps, ligneous particles, floor sweepings, etc.;
sediment including any bottom sediments of fresh or marine water systems; PA2 man-made mineral aggregate material and fill materials as well as man-made sediments arising in water-ways; and PA2 mineral residues from mining operations, such as those present in a tailings pond;
the words "fine" or "fines" shall be understood as referring to particles of soil having a diameter of not greater than approximately 250 .mu.;
the word "aggregate" and any similar word (whether as noun, adjective, etc.) shall be understood as referring to or as characterizing (or emphasizing) a "soil", "sediment", "material" or any portion thereof as a mass of individual particles or components of the same or varied size (e.g. the size of the components may be not uniform and may range from microscopic granules to 10 cm and larger); it is also to be understood that the particle size distribution of any particular soil mass, etc. may be different from that of another soil mass, etc.;
the words/expressions "contaminated", "metal contaminated" and the like, when used in relation to the words "soil", "sediment", "material" and the like, shall be understood as referring to that portion of the unconsolidated mantle (whether natural or man made) which is contaminated, in any way whatsoever, whether voluntarily or otherwise;
the word "lixiviant" shall be understood as referring to a reagent capable of extracting a soluble constituent (i.e. solubilizing) from a solid mass (i.e. the lixiviation of a material);
the words "decontaminate", "decontamination" and the like shall, in relation to metal contaminated material, be understood as referring to a process or the material produced by a process wherein the material or part thereof is provided which has a reduced level of metal as compared to the original material; and
the word "classification" and the like shall, be understood as referring to the dividing of an aggregate material into size groupings or portions and as including separation of constituent components in accordance with size, separation of constituent components by magnetic separation, disaggregation to reduce particle size followed (as desired or necessary) by magnetic separation and/or separation by size (e.g. size separation by screening, gravity separation, etc.).
Metal contaminants in aggregate consist of naturally occurring metals as well as man-made metals. The metal contaminants may be present as free or chemically combined species in any state of oxidation chemically possible. Metal contaminants include, for example, base metals, such as lead, zinc, mercury, cadmium, copper, nickel, chromium and cobalt, as well as other metals such as silver, molybdenum, selenium, arsenic and vanadium, etc. Metal contaminants also include radioactive metals (such as for example uranium, technetium, radioactive cobalt60, and plutonium) and other inorganic species (such as for example metal complexes based on arsenates, selenates, etc.) which when present in a soil are considered to be a contaminant.
The existence of metal contaminated aggregate material can lead to serious environmental problems. Improperly contained or decontaminated aggregate material can, for example, contribute to unsafe levels of metal(s) in surface and ground water as well as in the air (e.g. by contaminated dust). Contaminated aggregate material can thus affect the health and well being of people living or working in the vicinity of or who come into direct contact with such material.
Thus, the presence of contaminated aggregate on the sites of former or existing industrial complexes, for example, pose a particularly serious problem. Since such aggregate can pose a risk to the health of individuals, the presence of such soils can seriously affect the continued or alternate usage of such sites, e.g. redevelopment of a former industrial site for residential use may be precluded due to the presence of the contaminated soil.
Discarded mining aggregate is another source of contaminated aggregate. Previous mining operations were limited by the current technology of the time as to the amount of metals that could be extracted. As a result, discarded mining aggregate exists that could be further processed to extract more of the metal. However, the existence of the aggregate creates an environmental concern.
The related art discloses decontaminating aggregate by the use of physical mechanisms, i.e., segregation by classification; chemical mechanisms, i.e., accelerated chemical leaching; or a combination of both. The use of any of these mechanisms results in a clean fraction and a fines fraction. The fines fraction consists of small particles that are relatively highly contaminated per unit volume. This is due to the fines having a higher surface area per unit volume, relative to larger particles. The higher surface per unit volume offers more exchange and adsorption sites for the contaminants to bind to the soil. As a result, the fines fraction is also highly resistant to washing as the fines have already resisted previous soil washings.
As the fines fraction can reach 10% to 20% of the soil, treatment and disposal of it is a critical issue in soil decontamination. Therefore, a need exists to decontaminate the fines that result from the decontamination of aggregate material.